The invention relates to an image forming system including a printer for forming a color image or for forming a monochrome image having a decurl function to correct a curl on a sheet on which an image has been formed, a copying machine and a multifunction peripheral in which functions of the printer and the copying machine are compounded.
In recent years, a high-speed printer for forming monochrome images of an electrophotographic type and of a direct-transfer type, a copying machine, a multifunction peripheral having functions of the high-speed printer and the copying machine, a color printer of a tandem type, a color copying machine and a color copying machine having functions of the tandem type color printer and the color copying machine have come to be used widely. In these image forming apparatuses of an electrophotographic type, there are problems that a sheet is curled or transformed into a waviness shape, because the sheet loses moisture when it is in a fixing process.
As an image forming apparatus for solving the problems, Unexamined Japanese Patent Application Publication No. 05-309971 (FIG. 1) discloses an image forming apparatus having therein a decurl device, a sheet finisher and a controller, wherein curls of transfer material are removed by the decurl device. The sheet finisher carries out post-processing for the transfer material on which an image has been formed. The controller controls operation conditions such as pressing force of the decurl device for a sheet material, depending on a post-processing mode of the sheet finisher. Owing to the structure of this kind, efficient decurling (which will be also called decurl processing, hereafter) becomes to be possible, which improves a stackable property for sheet ejection.
Further, relating to an image forming apparatus that corrects curls of a sheet, Unexamined Japanese Patent Application Publication No. 2002-080157 (FIG. 1) discloses a curl correcting unit having therein an adjusting mechanism, a control device and a manual changing device, wherein, when correcting curls caused on a sheet on which images have been formed to deform them to be curved temporarily, the adjusting mechanism adjusts an amount of curls to be corrected. The control device controls an amount of curls to be corrected which has been adjusted by the adjusting mechanism to the setting condition that is prescribed in advance, depending on fixed parameter information such as a sheet type and image density. With the foregoing serving as an assumption, the manual changing device makes an amount of curls to be corrected adjusted by the adjusting mechanism to be changed manually. By constituting the apparatus in the aforesaid manner, it is possible to change manually, even when curl correction by automatic adjustment of an amount of curl correction is not carried out correctly, thus, proper curl correction can be realized in a simple and easy way.
In the meantime, there are following problems in an image forming system equipped with a post-processing unit equipped with decurl functions which correct curls on a sheet on which images have been formed.
In the image forming apparatus disclosed by Unexamined Japanese Patent Application Publication No. 05-309971, an operation condition such as a pressing force of a decurl device for a sheet material is controlled depending on a post-processing mode. In fact, full automation of optimum decurl setting is extremely difficult because sheet conditions, output conditions and image forming conditions affect intricately.
Further, in the case of a curl correction unit disclosed in Unexamined Japanese Patent Application Publication No. 2002-080157, a manual changing device is provided so that an amount of curl correction which has been adjusted automatically may be changed manually for the sheet having thereon images for which the decurl direction has been set. In general, the decurl direction is set for the conveyance direction for a sheet. However, the sheet is sometimes reversed or rotated depending on the selected post-processing conditions. It is therefore necessary to consider the conveyance path up to a sheet-ejection tray to which the sheet is ejected finally, for setting the desired decurl direction for the sheet. This makes it difficult to set the decurl direction easily.